Dyeing of textile fibers



a hast w.

a t-m DYEING oFrnXTrLE FHBERS Roy M. Rochester, Abbeyille, and John S. Beattie, Greenwood, S. Ctyassignors to Deering Millilten Research Corporation, a corporation of Deiawarc (No Drawing. Application Iuly 1953 b Serial No. 371,175

screams. (c1; ze a- 134 The fiber is currently new synthetic that the older, more conventional methods of dyeing were incapable of giving satisfactorypenetra tion and depth of color. 1

Probably the most'widely usedand most successful of the new dyeing methods for acrylicfiber is knownas the cuprous ion method. This method consists in add- .ing a cupric salt and a reducing agent to a bathcontainingthe fiber and an acid dye and maintaining the bath at or very near the boiling point duringthedyeing operation. It is known that in this method the copper sulfateand the reducing agent react within the bath to produce copper in the cuprous valence state. lt'isaithecrized that thecuprous copper is then absorbed. by. the acrylic fiber thereby creating an iafifinity for acidydyes. Despite the success of this method it has several disadvantages. The greatest disadvantage results from the .ifact ,that addition of the reducing agent to the dye bath is very critical andas a result it -has been necessary to devise rather elaborate methods for controlling the "addition of the reducing agent. One such control is No. 3, pgs. 76' to 80, wherein there is presented a brief review of the cuprous ion method of dyeing. lt canbe seen from this publication that the cuprous ion method is undesirably complicated and that close control is required order to obtain satisfactory results. b

t In viewof the difficulties in practicing the cuprous ion :method, it is anobject of the present invention toprovide .a method for dyeingacrylic fiber which does not require thecomplex controls of the former method.

. discussed in theArnerican Dye Stuff Reportenfvol. II, r

b and RoracylVioIet ZR (DuPont). b b In practicing the invention it is first necessarysto provide a suitable. dyebath which is done by dissolving 2,779,726 H Patented Jan. 29, 195 7 per age of the current, the. bath is then ready for, the actual dyeing operation which may be performed incon- .ventional manner and which usually comprises. the mere immersion of the fiber in the dye bath for thereguisite length of time until the desired depth ofcolor has been obtained. lr'eferably; as in most cases of dyeing with an acid dye, thebath is maintained at or near the boiling temperature of the bath. t M

Ithas been found that the passage of the alternating currentafter a certain point isno longeressential and that it may be discontinued after the dye bath has been properly prepared; However, if it is desired to utilize the heating effect of; the alternating current, it is, of

course, permissible tocontinue the passage of the current during the dyeing operation.

, The process is applicable to staple fiber prepared iroin yarious polymersand copolyrners of acrylonitrile. The eopolyniers frorn which the fiber can be prepared include :copolyrners of acrylonitrile with suchcompounds as, for example, vinyl acetate, vinyl chloride, esters or other derivatives of acrylic or methacrylic acids, styrene,

methyl vinyl ltetouea or othersimilar polymerizable monomers. In generah the copolymers contain not more than. 15% of the aforesaid monomers,

t e uyeswhich can be satisfactorily appiied in the practice, of this invention include all of, those known as acid dyes. These area .well recognized class of dyes which are commerciallyavailable and which are characterized by their application from an acidic, dye bath.

Such dyes include, for example, Anthraquinone Blue Sky (c. I. 1088), alAnthraquinone Green GN 0.1. 1078),

. Grange ll (C. 1. U1), Quinoline Yellow PN (Cal. 802),

Anthraquinone Blue RA.(Du Pout), Anthracene Blue WR (l, 2 i, 5, 6, 8-hexahydroxyanthraquinone), aswell as many other dyes. Suitable. acid dyes are also sold nnder various tradenames. such as Roracyl Orange 5R 1 (Du Pont), Roracyl Dark. Green B (Du Pont), Pon tacyl FastRed AS ((1.1. 176 Pontacyl Rubine R (C. I. 179) predetermined. amounts of antacid dyeand a cupic salt inwater. The concentration of the dye in the solution is not critical and :almost any amount ofrdye can. be employed. Generally however, it is preferred to dissolve an amount of dyeequal tofron about 0.5% to about 20% by Weight of the material in accordance with conventional dyeing practice. The amount of cupricsalt to be employed isdependent upon the amountof dye in the bath. Thus within fairly critical limits,-the amountof cupric saltshould be equal to from about 40 to about170 by weight of the dye in the bath. .Amountsmf cupric salt above the stated range are unsatisfactory because during the later dyeing operation the yarn will acquire It is a, further object of theinvention to provide a it rnethod for dyeing acrylic fiberwhich is considerably faster than the previously known 'cu p rous ion method.

It is Still another objectof the invention to provide a method for dyeing acrylic fiber which does not require the addition of a reducing agent to thedye bath,"

The method of the present invention isbased on the discovery that a bath containing an acid dye and a *cupric salt can be rendered suitable for dyeing acrylic "fiber by passing an alternating electridcurrent through "the dye bath minute the actual dyeing operation.

In the process of this :invention, a bath containing an acid dye and a cupric salt is subjected to the passage of an alternating electric current. After the passage of .the alternating current for a certain length of time, which will vary with the volume otthe dye bath, the ingredients 2 .of the bath, the temperature of the bath and the ama coppery. tint ,andlan undesirable stiffness. Amounts of cupricsalt below the stated range are not particularly harmful but there will not be obtained during the dyeing operation the desired exhaustion of the dye. it is mentioned at this point that the amount of cupric salt will vary somewhat within the above range depending on the particular dye that is being used and on the particular cupric salt that is being employed. With niany dyes the optimum amount of cupri c salt to be used is about by Weight of the dyeland with other dyes the amount of cupric salt can easily be deterrnined by simple experi- ,nientation.

salt that is Water-soluble. By far the best results f rom the standpoint. of shade, and penetrationcan be obtained using copper sulfate and for this reason it is preferred to employ this compound. Satisfactory dyeings can also be obtained. however, by the use of such cupric salts as copper nitrate, copper acetate and cupric chloride.

After the solution of ingredients in the bath, it is prepared for the dyeing operation by the passage of an alterhating electric current therethrough. The passage of the alternating current is conveniently accomplished by imm'er'sin'g electrodes in the dye bath and connecting one of the electrodes to a suitable source of alternating current and grounding th'e'other electrode. The best results in the present invention are obtained using copper elec trodes but the material of which the electrodes are made does not seem to be especially critical.

' The principal variable affecting the amperage of the alternating current to be employed is the volume of the dye bath. -It has been found that the amperage varies in direct proportion to the volume of the liquid. For example in a bath containing about 125 gallons of liquid it has been found'that amperages between 100 and 1000 amperes can be used although for a bath of this size it is preferred to employ an amperage between about 300 and 500 'amperes. From this knowledge it is possible to calculate directly the amperage which will be required for a'bath of almost any other size. Assuming, for example,

that the bath contains approximately one-half of 125 gallons, then approximately one-half of the amperage required fora 125 gallon bath will be needed. The only exception to this rule is in the case of small baths of laboratory size, i. e., from about /2 to 5 gallons, wherein currents of from about to ameres are preferred.

The amperage will also vary with the number of electrodes. Thus, if there is provided a plurality of electrodes arranged in a sandwich fashion with the outermost electrodes being connected for a flow of alternating voltage and the inner electrodes being merely suspended between the outer electrodes, the amperage required will be reduced in inverse proportion to the number of cells. For example, a series of three electrodes will provide two cells and there will be required only one-half the number of amperes that would be required for a system having only two electrodes. It is believed that the reason for this phenomenon is the fact that the greater the number of electrodes and consequently the greater the number of cells, the greater will be the degree of ionization of the ingredients of the dye bath.

The preparation of the dye bath by the passage of an alternating electric current therethrough is preferably performed at or near the boiling point of the dye bath since at the boiling point of the dye bath the time of passage of the alternating current is materially reduced, the length of time required for the'electrical preparation'of the bath being a function of the temperature of the bath.

The duration of the passage of the alternating current is also a function of the volume of the dye bath and the amperage. It is, therefore, not possible to establish definite periods of time which will accomplish the necessary preparation of the dye bath in all instances. However, it has been found that for a dye bath of commercial size, i. e., about 125 gallons, passage of the alternating current for about two hours while the dye bath is at its boiling point is sufficient. Under the same conditions in laboratory size vessels of approximately one gallon, about ten minutes suffices for the passage of the alternating current.

In determining the duration of the passage of the alternating current, it has been found that the passage of the current is accompanied by a lowering of the pH of the dye bath. For example, in a dye bath containing Roracyl Dark Green 13 and copper sulfate, the pH is lowered from about an initial 3.5 to about 2.6 at which point the preparation of the dye bath is complete. The

I pH measurement, therefore, aifords a convenient method for determining the moment when the dye bath is properly prepared for the dyeing operation. However, the pH varies according to the ingredients of the bath and the pH figures stated above are applicable only to the combination of Roracyl Dark Green B and copper sulfate. The actual pH change for each different dye bath can best be determined by the experimental dyeing of yarn samples after varying periods of alternating current passage. In this manner, a pH change for each dye bath can be established and there is thus provided a simple and convenient method of control which can be employed in all subsequent dyeings with the same bath.

After the dye bath has been subjected to the passage of an alternating current for the required length of time in accordance with the considerations mentioned above, the bath is ready for the actual dyeing operation. In this operation no special precautions are necessary and satisfactory dyeings can be obtained quite rapidly by merely immersing the yarn or fabric to be dyed in the boiling dye bath and sufiicient yarn can be dyed to substantially exhaust the bath. Any of the customary and conventional pieces of apparatus that are presently employed in the dyeing of staple yarn or fabric can be employed. The length of time for the immersion of the yarn or fabric is subject to many considerations and will vary according to the temperature of the dye bath, and the depth of shade desired.

Very little is known of the mechanism by which the alternating current modifies the dye hath so that it is rendered suitable for the subsequent dyeing operation. However, it is known that satisfactory dyeing cannot be obtained Without the preliminary treatment with the alternating current so that it is reasonably certain that a chemical change of some kind occurs within the bath. It has also been determined that direct current is completely unsuitable in the method of this invention since the use of direct current invariably results in a deposition of copper in the bath and on the fiber.

Various conventional dyeing assistants, surface active agents, or the like, may be added to the dye bath if desired. For example, in some instances improved results may be obtained by adding a carrier of the type conventionally employed in the dyeing of acrylic fibers, as illus trated by p-phenylphenol, o-phenylphenol, diphenyl and benzoic acid.

0 In order to illustrate the invention and its attendant advantages, the following examples are given.

Example 1 A dye bath was made up by dissolving the following ingredients in 500 ml. of water:

Grams Roracyl Dark Green B (Du Pont) 1 Anthraquinone Blue SWF (Pr. 12) 0.2 Du Pont Orange R0 (C. I. 161) 0.1 Copper Sulfate 3 The bath was then heated to its boiling point (approximately 213 F.) and two copper electrodes, each having an area of about 10 square inches, were immersed in the bath. A sixty cycle alternating current (10 .amperes) was then passed between the electrodes for a period of ten minutes while the bath was maintained at its boiling point. The current supply was then shut off and the electrodes were removed. During the passage of the current the pH of the bath was lowered from 3.5 to 2.1.

A skein of orlon staple yarn which had been previously scoured was then immersed in the dye bath with constant stirring, still maintaining the temperature of the dye bath at the boiling point. After an immersion time of about 5 minutes, the yarn had acquired an excellent black color. The penetration of the dye was also excellent. The color was fast to repeated washings.

Example 2 Grams Roracyl Dark Green B (Du Pont) 40 Anthraquinone Blue SWF (150%) (Pr. l2) Du Pont Orange R0 (C. I. 161) 3.75 Copper sulfate 37.5

Two copper electrodes, each having an area of about 32 square inches, were immersed in the bath with a space about Vs inch between electrodes. A sixty cycle alternating current was passed between the electrodes to give an amperage of 35 amperes and with the aid of external heating elements the temperature of the bath was raised to the boiling point of approximately 213 F. After passage of the electric current for /2 hour at the boiling point of the dye bath, the pH of the bath dropped from about 3.5 to about 2.1.

A package or orlon staple yarn weighing about 1 lb. which had been previously scoured was then dyed in the bath using a 1 lb. package dyeing machine, a conventional piece of equipment in the industry. During the dyeing operation the passage of the alternating current was continued and the heat therefrom was utilized to help maintain the bath at the boiling point. After approximately 30 minutes on the machine the yarn was dyed a good black; the penetration of the dye was excellent and the color was fast to washing.

Example 3 The procedure of Example 2 was followed substituting copper nitrate for the copper sulfate. Again a good dyeing was obtained but the penetration of the dye was somewhat poorer than in Example 2.

Example 4 The procedure of Example 2 was followed except that a series of six electrodes in which the four central electrodes were suspended between the two outer electrodes was employed in place of the pair of electrodes used in Example 2. This enabled the amperage of the alternating current to be reduced to about Vs of the amperage employed in Example 2. The dyeing of the yarn was performed as in Example 2 and an excellent shade of black was obtained.

The foregoing examples demonstrate the simplicity of the process of the present invention and its advantages. It is to be noted particularly that no extensive controls are necessary during the dyeing operation and that the dyeings are fairly rapid.

We claim:

1. A method for dyeing acrylic fiber which comprises subjecting to the passage of an alternating electric current an aqueous dye bath containing an acidic dye and an amount of a water-soluble cupric salt equal to about from 40 to by weight of the dye, and thereafter dyeing acrylic fiber in the dye bath.

2. A method according to claim 1 in which the cupric salt is copper sulfate.

3. A method for the dyeing of acrylic fiber which comprises subjecting an aqueous dye bath containing an acidic dye and a cupric salt in an amount equal to from about 40 to about 70% by weight of the dye to the passage of an alternating electric current, the amperage of the alternating current being based on the volume of the aqueous solution and being equivalent to from about to 1000 amperes for a bath of gallons and thereafter dyeing acrylic fiber in the bath.

4. A method according to claim 3 in which the cupric salt is copper sulfate.

5. A method according to claim 3 in which the entire process is carried out at a temperature approximating the boiling point of the bath.

6. The method for preparing a dye bath capable of dyeing acrylic fibers without the addition thereto of a reducing agent which method comprises subjecting an aqueous dye bath containing an acidic dye and an amount of a water-soluble cupric salt equal to about 40% to 70% by weight of the dye to the passage of an alternating electric current.

7. A method according to claim 6 wherein the amperage of the alternating current is from about 100 to 1,000 amperes for each 125 gallons of dye bath.

8. A method according to claim 7 wherein the dye bath during the passage of the electric current is at a temperature approximating the boiling point of the bath and the bath is subjected to the alternating current for a period of about at least 2 hours.

9. The method of claim 8 wherein the cupric salt is copper sulfate.

OTHER REFERENCES Du Pont Technical Bulletin, vol. 7, No. 1 (March 1951), pp. 45-52. 

1. A METHOD OF DYEING ACRYLIC FIBER WHICH COMPRISES SUBJECTING TO THE PASSAGE OF AN ALTERNATING ELECTRIC CURRENT AN AQUEOUS DYE BATH CONTAINING AN ACIDIC DYE AND AN AMOUNT OF A WATER-SOLUBLE CUPRIC SALT EQUAL TO ABOUT FROM 40 TO 70% BY WEIGHT OF THE DYE, AND THEREAFTER DYEING ACRYLIC FIBER IN THE DYE BATH. 